Volume control



Nov. 24, 1931. v. c. MACNABB 1,833,085

I VOLUME CONTROL Filed Aug. 18, 1950 Patented Nov. 24, 1931 UNITEDSTATES PATENT OFFICE PENNSYLVANIA, ASSIGNOB TO ATWATEB PHILADELPHIA,PENNSYLVANIA, A COR- VOLUME CONTROL Application filed August 18, 1930.Serial No. 478,013.

My invention relates to radio-receiving systems utilizing thermionictubes for the amplification of radio-frequency signal energy, andparticularly to systems of such character which include a source ofcommercial alternating current for supplying current to electrodecircuits of the tubes.

In accordance with my invention, control of the volume or amplitude ofreproduction is efi'ected by varying both the amplificationcharacteristic of the radio-frequency amplifier tubes and the transferof radio-frequency signal energy to or between the amplifier tubes;preferably, and to ensure high ratio of signal to noise and eliminationof noises due to improper operating conditions of the amplifier tubes,the volume is first reduced by suitably modifying the amplificationcharacteristic, for example by increase of ,the negative grid biasingpotential, with insubstantial or no change by reduction of the enertransferred, and to effect further reductlon in volume, the transfer ofsignal energy is lessened with decreasing or insubstan- =tial effect bymodification of the amplification characteristic; more specifically, inseeking suitably low volume, it is provided that the negative grid biascannot be adjusted to such high value that the ampl ifier tubes aremodulating or have a detecting action on the received signals.

Further in accordance with my invention, the control of both theamplification characteristic andthe transfer of signal energy isvariable by a single adjustable element, as a knob or dial. In someforms of my invention, the knob, or equivalent, is mechanically coupledto movable contacts adjustable along independent resistances, one ofwhich, for example, may be in circuit with, as in shunt to, a couplingelement, and the other of which may be in circuit between the grids andcathode of one or more of the tubes, while in another form of myinvention, the volume control knob is mechanically connected to themovable contact-of a single resistance, which more specifically. isin'shuntto a coupling element, as the primary winding of a transformer,and also common to the grid and anode circuits of one or more of thetubes.

'My invention further resides in the methods, systems and featureshereinafter described and claimed.

For an understanding of my invention and for illustration of some of thevarious cirapparatus with power supply and reproducer;

Fig. 3 is a wiring diagram of a modified form of my invention.

Referring to Fig. 1, signal energy received by the absorption or antennastructure A is impressed upon the input circuit of a radio frequencyamplifier tube V and preferably again amplified at radio frequency byone or more tubes V1, V2, etc. Adjustment of the contact G alongresistance R varies the amount of resistance or impedance in shunt tothe input element L of the tube V, which may be the winding of atransformer, or, as indicated, a coupling impedance. By adjusting theposition of contact C, the amount of energy transferred, and ultimatelythe volume of reproduction, is controlled, the transfer decreasing asthe contact C approaches the antenna end of the resistance and viceversa. However, this simple control is not satisfactory for the controlof volume of strong signals, as when the contact 0 is moved to includebut a small portion of the resistance R in shunt to the input element L,and the amplification of the tubes V, V1, etc., maintained high, theratio of signal to noises incident to high amplification by thermionictubes, is low.

To control the amplification characteristic of the radio frequencyamplifier tubes, contact C may be adjusted along resistance R1, which isincluded in circuit between the grids and the cathodes f of, forexample, the tubes V and V1. The resistance is traversed by currentflowing from the cathode to the grid terminal of the resistance so thatthe grids of the tubes are negative with respect to their cathodes.Adjustment of the contact G varies the amount of resistance R1 traversedcreased to such an extent that the tube is working on a curved orrectifying portion of its characteristic, resulting in unsatisfactoryoperation, particularly when, as indicated, the tubes are supplied froman alternating source, as there then resultsmodulation of the incomingsignal, causing hum and distortion. To maintain high ratio of signal tonoise and high quality of reproduction, I first decrease theamplification eifected by the tubes by increasing the negative grid biasbut not to such extent that they are working on a curved portion oftheir characteristic and effect further reduction of volume by changingthe transfer of signal ener These results may be obtained by com iningthe two above described and individually unsatisfactory controls ashereinafter set forth.

Preferably the contact C is connected to earth or equivalent to which isconnected the negative terminal of the source of grid bias andpotential. For example, the negative terminal of the B battery orequivalent supplying plate-current may be connected to earth so that theanode current reversing the resistance is utilized in. that portion ofits path between cathode and. earth to provide a grid bias potential. Asthe contact C is rotated in counter-clockwise direction, Fig. -1, theamount of resistance traversed by the anode current, and therefore thenegative potential applied to the grid G, is increased. The choice ofthe value of resistance R1 depends upon the amount of current flowingthrough it, the characteristics of the tubes utilized, etc., and is sochosen that when the contact C has been turned in counterclockwisedirection to the grounded terminal of resistance R1, the grid bias isnot so high that the tube is operating upon a curved portion of itscharacteristic, for example its grid-voltage plate-currentcharacteristic.

.For instance','it may have a resistance of the order of 6000 ohms, andthe resistance of R may be of the order of 2000 ohms. Both of theresistances are or may be wire-Wound, and may be more or less inductive,though either or both may be non-inductive.

The resistance R2 in circuit between the unground terminal of resistanceR1 and the cathodes f of the tubes is of such value that when thecontrol contact C is in maximum volume position, i. e., at the:ungrounded end of resistance R1, the biasing potential applied to thegrids of the tubes is not too low or satisfactory operation.

Accordingly, to reduce the volume of strong signals, the contact C isrotated in a counter-clockwise direction in engagement with resistanceR1 to increase the negative grid bias. As the contact C passes beyondthe grounded terminal of resistance R1, the negative bias remainsconstant at the predetermined maximum value, and the value of resistanceR, in shunt to the input element L, is progressively reduced, lesseningthe transfer of energy from the antenna circuit to the input circuit ofthe tube V.

It will be understood that the resistance R and R1 may be mounted forsuccessive engagement by the contact C or may each have its own contactarm, the arms being so mechanically connected that upon rotation of avolume controlling knob the amplification is first reduced b adjustmentof the contact along resistance 1 and subsequently further reduced byadjustment of a contact along resistance R. With the latter arrangement,the contact arms or the resistances may be so staggered that control ofvolume may be simultaneously effected by change in the amplification andthe transfer of signal energy, although in any event I prefer that inthe reductlon of volume the change in volume be effected preponderantlyby decreased amplification and subsequently preponderantly by decreasein transfer of signal energy.

While for purpose of illustration the 1"e sistance R has been shown inthe system coupling the antenna to the input system of the first tube,it will be understood that it may be an interstage coupling system, forexample, in shunt to the primary P of the transformer T coupling thetubes V and V1. When the tubes are of the type utilizing a uni-potentialcathode raised to electron emitting temperature by heaters supplied, forexample. with alternating current, the end of resistance R2 remote fromresistance R1 will be connected to the uni-potential cathode. Inreceiving apparatus utilizing screen grid tubes, the resistances R1 andR2 may be in cluded in the control grid circuit exactly as in Fig. 1, inwhich the tubes shown are of the triode type.

Theyolume control of Fig. 2 is essentially the same as that of Fig. 1.The resistance R, in shunt to the input element L, is variable byadjustment of the contact C for Varying the transfer of signal energy.The magnitude of resistance R1 may be varied by adjustment of thecontact C1 to change the bias supplied to the grids of the radiofrequency amplifier tubes. Adjustment of the volume control knob Kefiects simultaneous movement of the contacts C and C1. In moving theknob counter-clockwise to reduce volume, the change of resistance R isat first of little or no effect, but becomes increasingly effective asthe contact C approaches the antenna terminal of the resistance. Thesimultaneous movement of the contact G1 at first is predominant inefiecting control of volume as the change in the bias potentialappliedto the grid rapidly decreases the amplification". Al-

though the contacts C and C1 are mechani cally coupled to simultaneouslychangethe values of both resistance R and R1, the change of resistanceof R1 at first preponderates in reducing Volume, While subsequently thechange of resistance R preponderate in a control of volume. The effectupon the ear is a smoothly continuous change of volume with no marringof the reproduction by tube noises due to high amplification,distortion, or by hum, etc. The circuit positions of the tworesistances, one of which controls amplification and the other of whichcontrols energy transfer, may be varied without departing from thespirit and scope of my invention.

The signal energy impressed upon the input elementL is amplified by thetubes V, V1 and V2 at radio frequency, then rectified by the detectortube V3 and the resulting audio frequency current amplified by tubes V4and V5, the last of which includes in its output circuit the loudspeaker D, or other reproducing apparatus. Current for all of the tubesmay be supplied from a transformer 6 who e primary p is connected to asuitable source of alternating current of commercial voltage andfrequency, although suitable batteries may be employed. The terminalof-resistance I R2 remote from resistance R1 is connected to a point ofuni-potential determined, for example, by a center tapped resistance rin shunt to the secondary s1 supplying current to the cathodes of thetubes V. V1 and V2. The plate-current of these tubes, supplied by thesecondary .92 of the transformer and'the rectifier through a suitablefiltersvstem, traverses the resistance RQand that portion of resistanceR1 between the contact C1 and the terminal connected to resistance R2.'It will be understood that the biasing potential 1 may be derived inother ways. (For example,

resistances R1 and R2 maybein circuit with a' bleeder resistance acrossthe filter circuit. with suitable connections to the grid and cathodestructure of one or more of the tubes, or alternatively, the resistancesR1 and R2 may be connected across a properly poled C battery.)

In the modification shown in Fig. 3, a single resistance R3 has oneterminal 7" connected to the cathodes of the tubes V and V1 and itsother terminal h is connected to the high potential end of the inputelement L, which in the example specifically'shown is the primarywinding of an autotransformer coupling the antenna circuit to the inputof the tube V.

That portion of resistance R3 between the contact C and the point Itcorresponds to resistance R of the preceding modifications,

and that portion of the resistance between the contact and its terminalf corresponds to the resistance R1 of the modifications previousldescribed. In reducing volume the contact is turned in counter-clockwisedirection progressively reducing the section B and thereby increasingthe shunting effect upon the input element L1. At first the ratiobetween the v impedance of the input element L and imsense to reduce thevolume. When the con-' tact C is moved away from the terminal f, theamplification at first changes rapidly but the change becomes less andless as the contact C approaches the other terminal of the resistance.

The resistance'of R3 may be of the order of 200.0 ohms although it willbe understood that the value may vary considerably there rom.

It will be understood that when my invention is utilized in othercircuit positions, it may be necessary to use blocking condensers toprevent short circuiting of direct current through the resistance R. Forexample if in Fig. 3, the terminal h of resistance R3 is connected tothe plate end of the primary p of transformer T to control the energytransfer between the output circuit of tube V and the input circuit ofV1, there should be in- At the same time that the section B cluded inthis connection a condenser of suit- I able low impedance toradio-frequency currents. A

What I claim is:

-1. In the operation of radio-receiving apparatus utilizing thermionictubes for amplifying or repeating radio-frequency signal ,11'.) energy,the method of reducing the volume quencysignal energy between limitswithin which high ratio of signal to noise obtains,

and simu taneously varying the amplification characteristic of one ormore of said tubes within limits between which the curvature of thegrid-voltage plate-current characteristic is not pronounced.

3. In the operation of radio-receiving apparatus utilizing thermionictubes for ampliying or repeating radio-frequency si nal energy, themethod of reducing the v0 ume or amplitude of signals which comprisesmodifying the amplification characteristic of one or more of said tubesto decrease the amplification of signal energy, and simultaneouslydecreasing the transfer of signal ener the reduction at first beingpreponderant y by decrease of amplification ,and subsequentlypreponderantly by decrease of transferred signal energy.

4. In the operation of radio-receiving apparatus utilizing thermionictubes for amplifying or repeating radio-frequency signal energy, themethod of reducing volume or amplitude of signals which comprisesincreasing the negative potential applied to the grid structure of oneor more of said tubes but not to such extent that the curvature of thegrid-voltage plate-current characteristic is pronounced, and thereafterdecreasing the transferred signal energy for further reduction involume.

5. In the operation of radio-receiving a paratus utilizing thermionictubes for amp ifying or repeating radio-frequency si al energy, themethod of effecting contro of volume or amplitude of reproduction, whichcomprises varying the biasing potential ap-- plied to the grid structureof one or more of said tubes, and simultaneously varying a shuntingeffect upon a coupling element effective in transfer of signal ener theeffect of variation of biasin potentlal' preponderatin in one part ofthe range of volume contro and the effect of shunting the couplingelement preponderating in another part of the volume control range.

6.. Radio-receiving apparatus comprising one or more thermionic tubes,rad1o frequency input and output systems therefor including couplinelements, and a volume control element a justable to vary both thebiasing potential of the grid of one or more of said tubes and themagnitude of transfer of signal energy by on or more of said couplingelements, the mo ement of said element varying the grid potential withinlimits between which the curvature of the grid-voltage plate-currentcharacteristic is not pronounced, and the transfer of signal energywithin limits between which high ratio of signal to noise obtains.

7 Radio-receiving apparatus comprising cascaded thermionic tubes,absorption structure, a plurality of radio-frequency coupling means forcoupling said absorption structure to the first tube of said cascade andthe input and output circuits of said tubes, and a volume controlelement adjustable both to vary the amplification characteristic of oneor more of said tubes and the transfer of signal ener by at least one ofsaid radio-frequency coupling means, movement of said element in oneportion of its range of movement effecting control of volume principallyby variation of the amplification characteristic, and in another portionof its range of movement efi'ecting control of volume principally bychan e in the transfer of signal energy.

8. Ba io-receiving apparatus comprising one or more thermionic tubes,radio frequency coupling elements in the input and output circuitsthereof, impedance in circuit with at least one of said coupling elementto vary the transfer of signal energy, a source of grid-biasingotential, and a volume control element ad ustable to vary both the effective magnitude of said impedance and the potential impressed upon thegrid of one or more of said tubes by said source of biasing potential,the movement of said element varying the grid biasing potential withinlimlts between which the curvature of the grid-voltage plate-currentcharacteristic is not pronounced, and the transfer of signal energywithin limits between which high ratio of signal to noise obtains.

9. Radio-receiving apparatus comprising one or more thermionic tubes,radio frequency coupling elements in the input and output circuitsthereof, a resistance in shunt to at least one of said radio-frequencycoupling elements to control the transfer of signal energy, resistancein circuit between the cathode and grid of at least one of said tubes,means for effecting flow of direct current through said secondresistance from the catlr ode terminal to the grid terminal thereof, anda volume control element adjustable to vary the effective magnitudes ofboth of said resistances, the movement of said control element in onepart of its range changing the volume preponderantly by variation ofgridbiasing potential, and in another part of its range changing thevolume preponderantly by variation of the transfer of signal energy.

10. Radio-receiving apparatus comprising one or more thermionic tubes,radio frequency coupling elements in the input and output circuitsthereof, a resistance in circuit with at least one of saidradio-frequency coupling elements, resistance in circuit between thecathode and grid of at least one of said tubes. means for effecting flowof direct current through said second resistance so poled that the gridof said tube is negative with respect to its cathode, and a volumecontrol element adjustable simultaneously to vary the effectivemagnitudes of said resistances, the movement of said control element inone part of its range changin the volume preponderantly by variation 0negative grid-biasing potential, and in another part of its rangechanging the volume preponderantly by variation of the transfer ofsignal energy.

' 11. Radio-receiving apparatus com rising one or more thermionic tubes,ra io-frequency coupling elements in the input and output circuitsthereof, a resistance in shunt to at least one of said radio-frequencycoupling elements, resistance in circuit between the cathode and grid ofat least one of said tubes, means for efl'ectin flow of direct currentthrough said secon resistance so poled that the grid of said tube isnegative with respect to its cathode, and a volume control elementadjustable simultaneously to vary in opposite senses the efi'ectivemanitudes of said-resistances cumulatively to e ect chan e in volume oramplitude of reproduction, tfie efi'ect of variation of one resistancepreponderatin for one part of the range of movement 0 said controlelement, and the effect of variation of the other resistancepreponderating for another part of the range of movement of said controlelement.

12. Radio-receiving apparatus comprising one or more thermionic tubes,radio-frequency coupling elements in the input and output circuitsthereof, a resistance in circuit with at least one of saidradio-frequency coupling elements, resistance in circuit between thecathode and grid of at least one of said tubes, means for effecting flowof direct current through said second resistance so poled that the gridof said tube is negative with respect to its cathode, and a contact armadjusta le along and engaging said resistances in succession, in controlof volume of strong signals from maximum to minimum, whereby initialmovement of said arm reduces volume by increase of the negativegrid-biasin potential, and subsequent movement of sai arm reduces volumeby decreased transfer of signal energy. a

13. Radio-receiving apparatus comprising one or more thermionic tubes,radio-frequency coupling elements in the input and output circuitsthereof, a resistance in circuit with at least one of saidradio-frequency coupling elements, resistance in circuit between thecathode and grid of at least one of said tubes, means for 'efiectin flowof direct current through said secon resistance so poled that the gridof said tube is negative with respect to its cathode, and a controlmember movable to increase the magnitude of said second resistance ininitial reduction of volume, and thereafter to decrease the magnitude ofsaid first resistance for further reduction of volume.

14. Radio-receiving ap aratus comprising one or more thermionic tu s,radio-frequency coupling elements in the in ut and output circuitsthereof, a resistance aving one terpreponderantly by change of negativeminal connected to a terminal of one of said coupling elements andanother terminal connected to the cathode structure of one or more ofsaid tubes, an adjustable contact movable along said resistance andconnected to another terminal of said coupling element and to thenegative terminal of a source of direct current effecting flow ofcurrent through that portion of said resistance between said contact andsaid cathode structure, whereby movement of said contact in one part ofits range effects control of volume idbias and in another part of itsrange e ects control of volume preponderantly by change in signaltransfer.

15. In the operation of radio-receiving apparatus utilizing thermionictubes for amplifying or repeating radio-frequency signal ener the methodwhich comprises controlllng the volume or amplitude of reproduction ofstrong signals throughout a range of volume partially by varying thetransfer of radio-frequency signal energy between limits within whichhigh ratio of si al to noise obtains, and partially by varying theamplification characteristic of one or more of said tubes within limitsbetween which the curvature of the grid-voltage plate-currentcharacteristic is not pronounced.

VERNON G. MACNABB.

